Resistance to gas
The internal tube is tested for chemical resistance. It is submerged for 72 hours in n-pentane at 23° C (as specified by the ISO 1817 standard). The specimen cannot change its volume by more than 20%, the change in resistance to stretching cannot exceed 25% and the change of overall stretching cannot exceed 30%. Later, after the hose has spent another 48 hours in the air at 40° C, its weight is tested. Compared to the initial weight, it cannot drop by more than 5%.
The external layer of the hose (the jacket) is tested in terms of resistance to n-hexane, into which the specimen is submerged for 72 hours (again at 23° C). As far as the external layer is concerned, more tolerance is allowed in terms of mechanical parameter changes than for the internal tube. Maximum volume change may be up to 30%, maximum stretching resistance change may be up to 35% and the maximum change of total length – also up to 35%.
Resistance to aging
The internal tube of the LPG hose, according to the 67 regulation, is also subject to the aging test as specified by the ISO 188 standard. The test procedure is such that the hose is exposed to temperature of 115° C for 168 hours (seven full days). If the operational temperature range for a given hose exceeds the -25 to 125° C scope (e. g. -25 to 130° C), the temperature for the test is set at 10° C below the hose's maximum operating temperature (e. g. 120° C instead of the standard 115° C). When the aging test is complete, in order to pass it the hose must not expose a change in resistance to stretching of more than 25%, while the change in overall length must not be greater than 30%.
According to the ISO 188 standard, the external layer is also tested for resistance to aging by exposing it to temperature of 115° C for 336 hours (14 days). When the test is complete, the resistance to stretching cannot change by more than 25% and the maximum length increase cannot change by more than 30%.
Resistance to ozone
In accordance with the ISO 1431/1 standard, a test of the hose's external layer's resistance to ozone is performed. Specimens stretched by 20% are exposed to air containing 50 ppm of ozone at 40° C for 120 hours. Once the test is complete, specimens are expected to show no signs of breakages.
LPG hose tightness
Tightness of LPG hoses is of crucial importance. The test procedure is such that a 1 m piece of hose is attached to a liquid propane tank at 23±2° C as specified in the ISO 4080 standard. Across a period of 24 hours loss of gas from within the hose is monitored. The test is considered passed if the loss is below 95 cm3 per 1 m of hose across 24 hours. This means that per hour the loss of gas must not exceed 3,96 cm3.
Hoses used in the automotive industry, including for autogas systems, are also tested in terms of resistance to fire using methodology specified by DIN standards. Hoses are expected to be self-extinguishable and while they burn, no harmful compounds can be emitted.
The length of a low-pressure LPG hose in a car rarely exceeds 1 m, which means the cost of the hose constitutes a minor fraction of the cost of the entire autogas system. Yet the list of requirements for this seemingly insignificant component is very elaborate. Apparently this is all for a good reason – if a collision occurs, autogas system components within the engine bay are often significantly dislocated and yet the autogas system hardly ever loses its tightness. This is also true for the low-pressure part of the system, whose components are connected with rubber LPG hoses. Stand by for the ultimate practical test!
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